Stereoselective Halogenation in Friedel-Crafts Acylation of 1-Acetylindoline with Chiral 2-(Methanesulfonyloxy)propionyl Chlorides

Abstract

The Friedel-Crafts acylation of 1-acetylindoline with (S)-2- or (R)-2-(methanesulfonyloxy)propionyl chloride, and aluminum chloride in dichloromethane at room temperature did not afford the expected (S)- or (R)-1-acetyl-5-[2-(methanesulfonyloxy)propionyl]indoline, but gave optically pure (R)- or (S)-1-acetyl-5-(2-chloropropionyl)indoline, whose stereochemistry at the asymmetric carbon was inverted during the reaction. Similar reaction of 1-acetylindoline with the same chiral acylating agents in the presence of aluminum bromide gave mainly the corresponding 2-bromopropionyl derivatives, but as stereo mixtures.